Overview

The Cayin RU6 is the first dongle to implement a discrete 24-bit R-2R ladder in a portable DAC/AMP. Launched in late 2021 at USD 249, it employs 96 ultra-precision low-TCR thin-film resistors (48 per channel), offers 3.5mm and 4.4mm outputs, supports PCM up to 384 kHz and DSD, provides OS/NOS modes, and uses a relay-driven resistor-array hardware volume control [3]. DSD input is internally converted to high-rate PCM for playback [1].

Scientific Validity

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Independent measurements show notable departures from transparency. With 16/44.1 and a 1 kHz tone in OS mode, THD+N stays around −66 dB (0.05%) across 0.5–1.5 V outputs [1], noticeably worse than the 0.032% @ 1 kHz, 0.5 V manufacturer spec [3], and accompanied by an irregular, HF-tilted noise floor [1]. In NOS mode, an inter-channel timing skew of ~0.5 sample (~11 µs at 44.1 kHz) is observed [1]. Reference Audio Analyzer reports 0.56 Ω output impedance and ~130 mW @ 32 Ω / 14.3 mW @ 300 Ω on the single-ended out [2]. Overall, RU6 measures well below modern sigma-delta dongles on distortion and noise.

Technology Level

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As the first portable discrete R-2R design, the RU6 showcases genuine engineering—96× 0.1% resistors, dual 6-layer PCBs separating digital/analog domains, and a 99-step relay-based analog volume array [3]. Nevertheless, the architecture does not achieve the state-of-the-art measured performance attainable by contemporary multi-bit sigma-delta designs.

Cost-Performance

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Comparator (cheapest equal-or-better): Truthear SHIO, a dual-CS43198 dongle with 3.5mm + 4.4mm outputs and hi-res support. Manufacturer claims THD+N < 0.0002% and SINAD 117 dB A-wt [4]. Official price USD 69.99 [4] vs RU6 at USD 249. Functions are equivalent from a user perspective, and (per specs) SHIO’s measured performance is superior.
Computation: 69.99 ÷ 249 = 0.28 → score rounded to 0.3.
If a cheaper equal-or-better option appears, CP should be recomputed accordingly.

Reliability & Support

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Cayin is an established brand with standard warranty/support typical of the portable audio segment. No widespread reliability concerns surfaced from public information. Long-term durability advantages of a discrete topology are unproven.

Rationality of Design Philosophy

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Despite its originality, RU6 exhibits measurable artifacts—elevated THD+N, irregular noise behavior, and NOS-mode inter-channel delay [1][2]. Given readily available, functionally equivalent dongles with much better measurements at far lower prices, the design intent prioritizing “vintage” traits is difficult to justify for high-fidelity reproduction.

Advice

Choose RU6 only if you specifically want R-2R behavior and accept its measured compromises. For transparency-focused, measurement-driven value, a modern dongle like Truthear SHIO (USD 69.99) offers equivalent I/O and superior objective performance at a fraction of the price [4].

References

[1] Archimago’s Musings, “REVIEW & MEASUREMENTS: Cayin RU6 R-2R USB Dongle DAC/Headphone Amp”, https://archimago.blogspot.com/2022/01/review-measurements-cayin-ru6-r-2r-usb.html, Jan 2022. Key conditions: 16/44.1, 1 kHz, OS/NOS, APx555. THD+N ≈ −66 dB (0.05%), NOS inter-channel skew ≈ 11 µs.
[2] Reference Audio Analyzer, “Cayin RU6: Single-ended Out — report for a newbie”, https://reference-audio-analyzer.pro/en/user-report-amp.php?id=3824 (simplified view at access). Key results: output impedance 0.56 Ω; ~130 mW @ 32 Ω; ~14.3 mW @ 300 Ω.
[3] Cayin Official, “RU6 — Features/Specs”, https://en.cayin.cn/features/7/124/488.html. Details: 96-resistor discrete 24-bit ladder, OS/NOS, 0–99 relay volume, 3.5/4.4, supported formats.
[4] Truthear Official, “SHIO — Portable DAC/AMP”, https://truthear.com/products/shio. Price 69.99 USD; dual CS43198; 3.5/4.4; manufacturer-stated THD+N < 0.0002%, SINAD 117 dB A-wt.

(2025.8.20)